The present application is directed to high frequency resonant inverter circuits that resonate at frequencies higher than fundamental switching frequency. More particularly, the present application is directed to the resonant inverter circuit that operates continuously from an open circuit condition at the lamp's output terminals to a short circuit condition at the lamp's output terminals and will be described with particular reference thereto.
To correct this problem, a power supply controller, such as UC3861 IC chip manufactured by Texas Instruments, is used to pulse the inverter “ON” and “OFF” to attain the zero-voltage switching and lower the power dissipation. Typically, the power supply controller derives power from a component of the resonant circuit or from the inverter output. Such tapping compromises the zero-voltage switching nature of the inverter. During open state mode, too much power is transferred to the power controller causing its regulator to dissipate excessive power. During the short circuit mode, too little power might be transferred to the power controller, causing activation of its under voltage lockout circuit.
It is desirable to supply power to the power controller that is independent of the lamp's state without excessive power dissipation and without causing the activation of the under voltage lockout circuit. The present application contemplates a new and improved method and apparatus which overcomes the above-referenced problems and others.